Rotate the Matrix
Reported by candidates from Cisco's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
Cisco's October OA threw this one at candidates and it's deceptively simple on the surface. You get a matrix, you need to rotate it. The trick isn't BFS as some forums claim. It's understanding whether you're rotating the entire matrix 90 degrees or spiraling through layers. Either way, there's a mechanical pattern that's easy to blank on under pressure. StealthCoder reads the exact input and output constraints, and hands you the rotation logic in real time so you don't waste 15 minutes on the wrong approach.
Pattern and pitfall
Matrix rotation almost always means 90-degree clockwise or counter-clockwise. The classic solution transposes the matrix, then reverses each row (or reverses then transposes, depending on direction). Time is O(n squared), space is O(1) if you rotate in place or O(n squared) if you build a new matrix. The BFS hint is a red herring unless the problem explicitly asks you to visit cells in spiral order, which is a different beast. Common pitfall: confusing transpose with rotation, or trying to rotate layer-by-layer and messing up indices. The mechanical step is rotate-transpose-reverse or transpose-reverse depending on which direction. StealthCoder catches whether the problem wants 90 degrees or arbitrary angles and gives you the exact sequence.
StealthCoder is the hedge for the one pattern you didn't drill. It runs invisibly during the screen share.
You can drill Rotate the Matrix cold, or you can hedge it. StealthCoder runs invisibly during screen share and surfaces a working solution in under 2 seconds. The proctor sees the IDE. They don't see what's behind it. If you're reading this with an OA window open, you're who this was built for.
Get StealthCoderRelated leaked OAs
This OA pattern shows up on LeetCode as rotate image. If you have time before the OA, drill that.
You've seen the question.
Make sure you actually pass Cisco's OA.
Cisco reuses patterns across OAs. If you're reading this with an OA window open, you're who this was built for. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Rotate the Matrix FAQ
Is this actually a BFS problem or is the hint wrong?+
BFS is rarely the answer for matrix rotation. The hint might refer to spiral traversal, which is layer-by-layer traversal, not BFS. If the problem asks for rotation, it's almost always transpose plus row/column reversal. Read the input and output examples carefully.
Can I rotate in place or do I need a new matrix?+
In-place rotation is possible and more efficient, but requires careful index math to avoid overwriting values you still need. If you're tight on time, build a new matrix. It's O(n squared) space but zero mental load.
What's the difference between 90-degree and arbitrary rotation?+
90-degree rotation is mechanical: transpose plus reverse. Arbitrary angle rotation (like 45 degrees) needs matrix math or trigonometry. Cisco likely asks for 90 degrees. Check the examples immediately.
How do I avoid off-by-one errors with indices?+
Write out a small 3x3 or 4x4 example by hand, label the indices, and trace through one full rotation. Index errors are the most common bug. Do this before coding.
Should I memorize both clockwise and counter-clockwise?+
Know the 90-degree clockwise pattern cold: transpose, then reverse each row. Counter-clockwise is reverse first, then transpose. One problem statement tells you which one. Don't overthink it.